The present invention relates to a tensioning device for applying tension to the wire of a coil winding machine when it is wound, and more particularly to a magnetic tensioning device in which the braking torque is applied to the tensioning pulley of the device by opposing a magnet and a magnetizable disc without contact therebetween. An adequate tensioning device has been available for conventional coil winding machines used for winding wire supplied from a supply bobbin onto a coil bobbin. This device applies a certain tension to the wire during the winding operation of the coil winding machine. In such a tensioning device there are basically included a main tension pulley to which a braking torque is applied, an absorbing lever for absorbing fluctuations of the wire tension during the winding operation and a second tension pulley provided at the swinging end of the absorbing lever, and tension is applied to the wire drawn through the main tension pulley and the second tension pulley. Conventionally, the braking torque applied to the main tension pulley has been generated by mounting a band brake around the periphery of a disc which is made to rotate integrally with the main tension pulley. Thus, control of the breaking torque has been obtained by regulating the pressure to the band brake.
In such a conventional tensioning device, necessary tensioning of the wire is possible to a limited extent by regulation of the wire tension, but there have been the problem that the pressure of the band brake might change after long use of the band.
Therefore an object of this invention is to provide a magnetic tensioning device in which braking torque is applied to the main tension pulley by opposing magnet and a magnetizable disc opposed to each without contact therebetween.
Another object of the present invention is to provide a magnetic tensioning device in which the braking torque applied to the main tension pulley may be chosen by regulating the distance between the magnetic and the magnetizable disc.
A still further object of this invention is to provide a magnetic tensioning device in which a the normal running torque at the time of generation of an abnormal tension may automatically be recovered.
Still another object is to provide a magnetic tensioning device in which unevenness of rotation of the main tension pulley may be prevented.